In clinical tests and the like, the Hct value of blood is measured as one index that helps to know properties of the blood (flowability, whether or not the subject has anemia, etc.). Furthermore, in blood component measurement such as measurement of a glucose concentration (a blood glucose level) in blood, a measured value may vary depending on a Hct value, so that the measurement of the Hct value might be required in order to correct the measured value. In general, the manual measurement of a Hct value is carried out, for example, by adding a blood coagulation inhibitor to blood, causing the blood to be drawn into a capillary tube, sealing one end of the tube with putty or the like, subjecting the tube to high speed centrifugation, and then determining the ratio of red blood cells to the blood as a whole as 100%, based on the height of the red blood cell column (such a method is called a “microhematocrit method”). Apart from the manual measurement, a Hct value also can be measured using an automatic blood cell counter. Examples of the method using an automatic blood cell counter include: those that recognize red blood cells as electrical pulses and calculate the Hct value from the sum of the sizes of the electrical pulses; and those that automatically calculate the Hct value from the average volume and the numbers of red blood cells. Incidentally, it is said that the standard Hct value of adult males is 39% to 50%, and the standard Hct value of adult females is 36% to 45%.
However, the conventional method for carrying out the manual Hct measurement has a problem in that it requires complicated operations and takes a long time. On the other hand, the Hct measurement method using an automatic blood cell counter has a problem in that it is necessary to use a special device. On this account, studies have been made to provide techniques for measuring a Hct value electrochemically and easily using a sensor (see Patent Document 1). However, the conventional method of measuring a Hct value using a sensor has a problem in its accuracy and reliability.    Patent Document 1: Japanese Patent No. 3369183